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Published on: October 15, 2018
Haploinsufficiency of Mdm2 and Mdm4 in tumorigenesis and development
Tamara Terzian1, Yongxing Wang, Carolyn S Van Pelt
1Department of Cancer Genetics, Box 1010, The University of Texas M. D. Anderson Cancer Center, Baylor College of Medicine, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
Abstract:
The tumor suppressor p53 is inactivated by multiple mechanisms that include mutations of the p53 gene itself and increased levels of the p53 inhibitors MDM2 and MDM4. Mice lacking Mdm2 or Mdm4 exhibit embryo-lethal phenotypes that are completely rescued by concomitant deletion of p53. Here we show that Mdm2 and Mdm4 haploinsufficiency leads to increased p53 activity, exhibited as increased sensitivity to DNA damage and decreased transformation potential. Moreover, in in vivo tumor development, Emu-myc Mdm4+/- mice show a delayed onset of B-cell lymphomas compared to Emu-myc mice. Additionally, Mdm2+/- Mdm4+/- double-heterozygous mice are not viable and exhibit defects in hematopoiesis and cerebellar development. The defects in Mdm2+/- Mdm4+/- mice are corrected by deletion of a single p53 allele. These findings highlight the exquisite sensitivity of p53 to Mdm2 and Mdm4 levels and suggest that some cell types may be more sensitive to therapeutic drugs that inhibit the Mdm-p53 interaction.
Insights
Reducing levels of p53 inhibitors MDM2 and MDM4 enhances tumor suppressor p53 activity. This suggests targeted therapies inhibiting MDM-p53 interactions may be effective in specific cell types.
Area of Science:
- Molecular Biology
- Cancer Biology
- Genetics
Background:
- The tumor suppressor p53 is crucial for preventing cancer but is often inactivated.
- Inactivation occurs through p53 gene mutations or increased levels of its inhibitors, MDM2 and MDM4.
- Complete absence of MDM2 or MDM4 in mice causes embryonic lethality, which is rescued by p53 deletion.
Purpose of the Study:
- To investigate the effects of partial loss of MDM2 and MDM4 on p53 activity and organismal development.
- To assess the impact of reduced MDM2 and MDM4 levels on tumor formation in vivo.
- To explore the therapeutic potential of targeting the MDM-p53 interaction.
Main Methods:
- Generating and analyzing mice with haploinsufficiency for Mdm2 and/or Mdm4.
- Assessing p53 activity through sensitivity to DNA damage and transformation potential.
- Evaluating B-cell lymphoma development in Emu-myc Mdm4+/- mice.
- Investigating developmental defects in Mdm2+/- Mdm4+/- double-heterozygous mice and their rescue by p53 deletion.
Main Results:
- Mdm2 and Mdm4 haploinsufficiency increased p53 activity, leading to heightened DNA damage sensitivity and reduced transformation.
- Mice with Mdm4 haploinsufficiency (Emu-myc Mdm4+/-) exhibited delayed B-cell lymphoma onset.
- Mice lacking both Mdm2 and Mdm4 (Mdm2+/- Mdm4+/-) were non-viable, showing hematopoietic and cerebellar developmental defects.
- These developmental defects were ameliorated by deleting one p53 allele.
Conclusions:
- p53 activity is highly sensitive to the levels of its inhibitors, MDM2 and MDM4.
- Partial inhibition of MDM2/MDM4 can enhance p53's tumor-suppressive functions.
- Specific cell types might be particularly vulnerable to therapies targeting the MDM-p53 axis.
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